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Residents and supporters stand outside Los Angeles City Hall during a demonstration ahead of the testimony before the Los Angeles City Council on the ongoing natural gas leak in the Porter Ranch area of Los Angeles, California December 1, 2015. Government and industry officials in Ontario say it's unlikely a similar event would happen in the province. (REUTERS/Gus Ruelas)

A leak of natural gas stored underground, on the scale of one that has forced thousands of southern California residents from their homes for months, is unlikely to happen in Lambton County, officials say.

The ground in Sarnia and Lambton County is home to a significant number of salt caverns and depleted wells used by the chemical and energy industry to store natural gas, other hydrocarbons and liquified petrochemicals.

This storage is a largely unseen but significant resource for industry in Sarnia-Lambton, and other regions.

In late October, a leak was detected in an underground natural gas field in the affluent Los Angeles neighbourhood of Porter Ranch, leading to thousands of residents having to leave their homes.

The cause of the leak is believed to be a broken injection-well pipe several hundred feet beneath the surface, and the company that operates the site hasn't been able to fix it yet.

In Ontario, storage wells are regulated by the Ministry of Natural Resources and Forestry.

“Due to Ontario's much more stringent regulatory requirements and lower pressures and volumes for storage, an event similar to that in California is extremely unlikely,” ministry spokesperson Jolanta Kowalski said in an e-mail.

The ministry regulates storage wells through a national standard setting out requirements for the design, operation, maintenance, safety, monitoring and testing, Kowalski said.

As well as extensive underground storage in Sarnia-Lambton's Chemical Valley, Dawn-Euphemia Township is home to a large natural gas storage and trading hub owned by Union Gas.

“Not all storage is the same,” said Andrea Stass, a spokesperson for Union Gas.

The underground storage pools Union Gas operates in Dawn-Euphemia are much smaller than those in California, she said.

“They're shallower, and they operate at a much lower pressure,” Stass said.

“Those things combined, significantly reduce the risk of a similar incident.”

The Union Gas wells in Dawn-Euphemia operate at an average pressure of approximately 1,1,00 to 1,500 pounds per square inch, about half of what's used at the California wells, Stass said.

The Union Gas storage wells pipes are encased in four layers of steel and concrete, plus an electrical current runs on the outside of the outermost casing to deter corrosion, she said.

“We have a very rigorous well maintenance program, and that includes regular inspection of all our storage wells,” Stass said.

“If we detect any metal loss or corrosion, we fix that before it becomes an issue.”

Union Gas began developing the Dawn Hub 70 years ago and now has 23 storage pools there.

“We've never had an incident,” Stass said.

The Dawn hub is a “significant asset” connected to major supply basins and pipeline systems across North America.

It supports Ontario's natural gas supply, and is also a market hub where companies buy, sell and trade natural gas, she said.

Dean Edwardson, general manager of the Sarnia-Lambton Environment Association, an organization made up of 20 industrial manufacturers, said underground storage wells are monitored, regulated and maintained.

“The likely of something coming up from those caverns is probably a little more remote than a natural phenomenon,” he said.

In June 2015, Lambton Shores officials declared a localized state of emergency after geysers of natural gas blew out of a creek at the Indian Hills Golf Course.

It was determined to a naturally occurring event, since there were no pipelines in the area, and no other man-made sources for the gas found.

The website of the Ontario Petroleum Institute notes there are 73 active storage caverns in Ontario, using 124 wells with a total storage capacity of 3.5 million cubic metres.

“This kind of infrastructure is obviously an asset, both in terms of product storage and raw material storage,” Edwardson said.

Pembina operates a facility near Corunna on a 1,000-acre underground storage site originally owned by Dow Chemical.

In an application to the province in early 2015, Pembina said it wanted to expand the facility's storage capacity by converting 11 currently unused salt caverns to hydrocarbon storage within the next 15 years.

That would increase on-site storage capacity at the facility from 10 caverns to 21, and 826,000 cubic metres to more than 2.2 million cubic metres, the company's application says.